U.S. Pat. No. 5,505,529 discloses a hydraulic brake pressure control system which has a check valve to evacuate air in the fluid circuits. This hydraulic brake system includes a first solenoid valve which selectively closes the fluid line between the master cylinder and the wheel brake and a second solenoid valve which selectively connects the fluid line extending between the first solenoid valve and the wheel brake with the reservoir circuit. The brake fluid flows from the main brake circuit into the reservoir circuit through the second solenoid valve. The system further includes a pump to return the brake fluid in the reservoir circuit back to the fluid line extending between the master cylinder and the first solenoid valve.
After assembling the hydraulic brake system, a vacuum pump is connected to the reservoir of the master cylinder to evacuate the brake system. Then the main brake circuit and the reservoir circuit are filled with brake fluid. In this brake system, a one-way valve is provided between the reservoir circuit and the main brake circuit so that air in the reservoir circuit can be evacuated to the main brake circuit without opening the second solenoid valve. The one-way valve is a gravity type valve which opens when gravity is applied to the valve. This one-way valve makes it unnecessary to open the solenoid valves electrically when evacuating air in the brake system.
However, the above mentioned brake system suffers from the disadvantage that it requires a special valve such as a one-way valve. This increases the complexity and number of parts of the system, and makes the system more expensive.